1. Field of the Invention
The present invention relates to an oscillation module using an oven controlled crystal oscillator (OCXO) or the like and, more particularly, to an oscillation module capable of reducing the noise of the oscillator.
2. Description of the Related Art
In wireless communication, high-rate data communication of several 100 Mbps to 1 Gbps is necessary to transmit a moving image or the like. For this reason, a synthesizer with excellent phase noise characteristics in a range of micro wave to millimeter wave bands is required.
As a signal source for this, an over-micro wave synthesizer is developing, and the final phase noise is equivalent to the double noise of the OCXO.
That is, in order to reduce the phase noise in the signal source such as the over-micro wave synthesizer, the reduction of phase noise in the OCXO is essential.
In a related art, for the purpose of reducing the noise, a filter is provided at a rear stage of the signal source, so as to reduce the noise.
Further, as a relating prior art, Japanese Patent Application Laid-Open No. 06-152453 (Patent Document 1), Japanese Patent Application Laid-Open No. 06-152454 (Patent Document 2), and Japanese Patent Application Laid-Open No. 2003-218712 (Patent Document 3) are disclosed.
Patent Documents 1 to 3 disclose filter circuits which are configured with a band elimination filter (BEF) and a band pass filter (BPF) with respect to input signals.
[Patent Document 1] Japanese Patent Application Laid-Open No. 06-152453
[Patent Document 2] Japanese Patent Application Laid-Open No. 06-152454
[Patent Document 3] Japanese Patent Application Laid-Open No. 2003-218712
Although a monolithic crystal filter (MCF) is appropriate for detuned noise elimination of several 10 kHz to several 100 kHz in order to realize noise elimination with the conventional filter, insertion loss increases and an input level is limited in the case of a narrow band. Therefore, degradation in carrier-to-noise ratio (CNR) at the output of the filter may occur.